The endogenous agonists of the cannabinoid receptors CB1 and CB2 include the fatty acid amide anandamide (AEA). AEA is hydrolysed to arachidonic acid by the membrane bound protein fatty acid amide hydrolase (FAAH). FAAH was characterized in 1996 by Cravatt and co-workers (Cravatt, Nature 1996, 384, 83). It was subsequently determined that FAAH is additionally responsible for the catabolism of a large number of important lipid signaling fatty acid amides including: another major endocannabinoid, 2-arachidonoylglycerol (2-AG) (Science 1992, 258, 1946-1949); the sleep-inducing substance, oleamide (Science 1995, 268, 1506); the appetite-suppressing agent, N-oleoylethanolamine (OEA) (Rodriguez de Fonesca, Nature 2001, 414, 209); and the anti-inflammatory agent, palmitoylethanolamide (PEA) (Lambert, Curr. Med. Chem. 2002, 9(6), 663).
Inhibitors of FAAH are being sought since such inhibitors elevate the concentrations of these endogenous signaling lipids and thereby produce associated beneficial pharmacological effects. There have been some reports of the effects of various FAAH inhibitors in pre-clinical models. Those effects include analgesic properties (see WO 02/087569, WO 04/033652); anxiety (Kathuria, Nat. Med. 2003, 9(1), 76); spasticity (Baker, FASEB J. 2001, 15(2), 300).
Results of research on the effects of certain exogenous cannabinoids also suggest that a FAAH inhibitor may be useful for treating various conditions, diseases, disorders, or symptoms. These include pain, nausea/emesis, anorexia, spasticity, movement disorders, epilepsy and glaucoma. To date, approved therapeutic uses for cannabinoids include the relief of chemotherapy-induced nausea and emesis among patients with cancer and appetite enhancement in patients with HIV/AIDS who experience anorexia as a result of wasting syndrome.
Apart from the approved indications, a therapeutic field that has received much attention for cannabinoid use is analgesia, i.e., the treatment of pain. Five small randomized controlled trials showed that tetrahydrocannabinol THC is superior to placebo, producing dose-related analgesia (Robson, Br. J. Psychiatry 2001, 178, 107-115).
A number of individuals with multiple sclerosis have claimed a benefit from cannabis for both disease-related pain and spasticity, with support from small controlled trials (Svendsen, Br. Med. J. 2004, 329, 253). Likewise, various victims of spinal cord injuries, such as paraplegia, have reported that their painful spasms are alleviated after smoking marijuana. A report showing that cannabinoids appear to control spasticity and tremor in the CREAE model of multiple sclerosis demonstrated that these effects are mediated by CB1 and CB2 receptors (Baker, Nature 2000, 404, 84-87). Phase 3 clinical trials have been undertaken in multiple sclerosis and spinal cord injury patients with a narrow ratio mixture of tetrahydrocannabinol/cannabidiol (THC/CBD).
Cannabinoids produced dose-related reductions in intraocular pressure (IOP) and therefore may relieve glaucoma symptoms. Ophthalmologists have prescribed cannabis for patients with glaucoma in whom other drugs have failed to adequately control intraocular pressure (Robson, 2001 supra).
In addition to the effects of a FAAH inhibitor on AEA and other endocannabinoids, inhibitors of FAAH's catabolism of other lipid mediators may be used in treating other therapeutic indications. For example, PEA has demonstrated biological effects in animal models of inflammation, immunosuppression, analgesia, and neuroprotection (Ueda, J. Biol. Chem. 2001, 276(38), 35552). Oleamide, another substrate of FAAH, induces sleep (Boger, Proc. Natl. Acad. Sci. USA 2000, 97(10), 5044; Mendelson, Neuropsychopharmacology 2001, 25, S36).
FAAH inhibitors are considered potentially useful in treating Alzheimer's Disease, schizophrenia, depression, alcoholism, addiction, suicide, Parkinson's disease, Huntington's disease, stroke, emesis, miscarriage, embryo implantation, endotoxic shock, liver cirrhosis, atherosclerosis, cancer, traumatic head injury, glaucoma, and bone cement implantation syndrome.
Other diseases or medical conditions that would potentially benefit from inhibition of FAAH activity, include, for example, multiple sclerosis, retinitis, amyotrophic lateral sclerosis, immunodeficiency virus-induced encephalitis, attention-deficit hyperactivity disorder, pain, nociceptive pain, neuropathic pain, inflammatory pain, non-inflammatory pain, painful hemorrhagic cystitis, obesity, hyperlipidemia, metabolic disorders, feeding and fasting, alteration of appetite, stress, memory, aging, hypertension, septic shock, cardiogenic shock, intestinal inflammation and motility, irritable bowel syndrome, colitis, diarrhea, ileitis, ischemia, cerebral ischemia, hepatic ischemia, myocardial infarction, cerebral excitotoxicity, seizures, febrile seizures, neurotoxicity, neuropathies, sleep, induction of sleep, prolongation of sleep, insomnia, and inflammatory diseases.
Neurological and psychological diseases or conditions that would potentially benefit from inhibition of FAAH activity include, for example, pain, depression, anxiety, glaucoma, nausea, emesis, loss of appetite, sleep disturbances, respiratory disorders, allergies, traumatic brain injury, stroke, generalized anxiety disorder (GAD), obsessive compulsive disorders, stress, stress urinary incontinence, attention deficit hyperactivity disorders, schizophrenia, psychosis, Parkinson's disease, muscle spasticity, epilepsy, dyskenesia, seizure disorders, jet lag, and insomnia.
Other diseases or medical conditions that would potentially benefit from inhibition of FAAH activity, include, for example, a variety of metabolic syndromes, diseases, disorders and/or conditions, including but not limited to, insulin resistance syndrome, diabetes, hyperlipidemia, fatty liver disease, obesity, atherosclerosis and arteriosclerosis.
FAAH inhibitors are potentially useful in the treatment of a variety of painful syndromes, diseases, disorders and/or conditions, including but not limited to those characterized by non-inflammatory pain, inflammatory pain, peripheral neuropathic pain, central pain, deafferentiation pain, chronic nociceptive pain, stimulus of nociceptive receptors, phantom and transient acute pain.
Inhibition of FAAH activity can also potentially be used in the treatment of a variety of conditions involving inflammation. These conditions include, but are not limited to arthritis (such as rheumatoid arthritis, shoulder tendonitis or bursitis, gouty arthritis, and aolymyalgia rheumatica), organ-specific inflammatory diseases (such as thyroiditis, hepatitis, inflammatory bowel diseases), asthma, other autoimmune diseases (such as multiple sclerosis), chronic obstructive pulmonary disease (COPD), allergic rhinitis, and cardiovascular diseases.
FAAH inhibitors are potentially useful in preventing neurodegeneration or for neuroprotection.
In addition, it has been shown that when FAAH activity is reduced or absent, one of its substrates, anandamide, acts as a substrate for COX-2, which converts anandamide to prostamides (Weber et al. J. Lipid. Res. 2004; 45:757). Concentrations of certain prostamides may be elevated in the presence of a FAAH inhibitor. Certain prostamides are associated with reduced intraocular pressure and ocular hypotensivity. Thus, FAAH inhibitors may be useful for treating glaucoma.